This invention relates to nuclear magnetic resonance (NMR) methods and apparatus. More specifically, this invention relates to a method and apparatus for monitoring respiration rate with an NMR scanner.
Acquisition of diagnostically useful images of the upper torso and abdomen utilizing NMR techniques is often complicated by motion-induced artifacts. The primary cause of motion is patient breathing. The source of these artifacts has been determined to be motion-induced phase and amplitude errors in the phase-encoding dimension when using Fourier transform imaging techniques, such as the one commonly referred to as "spin warp." Numerous approaches have been suggested for minimization of these artifacts. Among the approaches suggested are breath holding, various gating schemes which involve data acquisition during expiration/inspiration, or controlled shallow breathing. However, all of these techniques involve either patient cooperation or increased scan time based on the full breathing cycle. Specific drawbacks associated with the proposed conventional techniques are, for example, that respiratory gating requires additional equipment to generate the gating signals and generally prolongs the imaging time. Breath holding and shallow breathing may work well with the volunteers, but are difficult or impossible for seriously ill or incapacitated patients who are the most likely subjects for NMR imaging.
It is, therefore, a principal object of the invention to provide a method for the reduction or elimination of motion-induced artifacts by non-gated synchrony with the breathing cycle, while eliminating the shortcomings of the afore-described conventional techniques.